1. Technical Field
The present invention relates to a method and apparatus for breast self-palpation and detecting changes of mechanical properties in the breast tissue that are indicative of breast cancer and other breast pathologies accompanied by changes in tissue viscoelasticity.
2. Description of the Prior Art
Despite the clear advantages of annual mammography screening, less than half of American women have ever had a single mammogram. Limitations and constraints in wider and effective use of mammography include: high price of devices, large equipment size and weight, insensitivity to certain cancers readily detectable by palpation, limitations imposed by the safety aspects of the use of ionizing radiation, and patient discomfort.
Palpatory self-examination, widely advised and taught to women as means of preclinical testing, contributes substantially to early cancer detection. Women themselves, who bring the problem to their physicians, first detect a significant fraction of breast cancer. The major drawbacks of manual palpation include the necessity to develop special skills to perform self-examination, subjectivity and relatively low sensitivity. Women often do not feel comfortable and confident to make a decision whether there really are changes in the breast, and whether they should bring them to the attention of their doctors.
In order to increase the sensitivity of palpation and allow data acquisition and analysis, a number of devices for mimicking breast palpation to detect tumors have been described. For example, Frei et al., U.S. Pat. No. 4,250,894, describe an instrument for breast examination that uses a plurality of spaced piezoelectric strips which are pressed into the body being examined by a pressure member which applies a given periodic or steady stress to the tissue beneath the strips. A signal processor interrogates the output voltage of each of the strips and the output is displayed to produce a display characteristic that shows the presence of an inclusion in the breast tissue being examined. U.S. Pat. No. 5,524,636, issued to one of the inventors of the present disclosure, describes a method and apparatus for imaging a portion of the body tissue comprising a support for a portion of the tissue, and a force applying member that tends to deform the tissue relative to a reference position, while at the same time a pressure pattern distribution is generated indicating areas of greater pressure. U.S. Pat. No. 5,833,634 issued to Laird et al. discloses a tissue examination device that includes a transducer element for generating a signal in response to force imposed on the transducer element in accordance with the varying properties of the underlying tissue structure and circuitry for detecting a variation in the signal as an indication of a localized area of stiffer tissue within the tissue.
A number of breast examination devices for clinical use based on computerized mechanical palpation have also been described. U.S. Pat. No. 5,860,934 issued to one of the inventors of the present disclosure, discloses a method and device that enables detecting regions of breast tissue having a modulus of elasticity different from that of surrounding glandular tissue using a pressure sensing array. Detecting of breast tumors is based on analyzing features of the stress pattern on the surface of an examined tissue that is a deviation from a stress pattern for a relatively homogeneous normal tissue. U.S. Pat. No. 6,091,981 issued to Cundari at al. describes a device that includes sensors which produce signals in response to pressure imposed on the sensors as the sensors are pressed against the breast tissue. A location or a map of detected underlying tissue structure relative to a reference point is generated and displayed. U.S. Pat. No. 6,192,143 B1 describes a computer controlled apparatus for detecting breast tumors by mechanically palpating in a full surface scan manner in order to detect small lumps or other anomalies. A palpation finger is brought into pressure contact with a sequence of small areas across the entire breast. Concurrent with the palpation scan, a scan of breast color and temperature is conducted. U.S. Pat. No. 6,190,334 B1 discloses an apparatus for automated breast palpation including an actuator having an extendable probe for contacting the tissue and an electronic control module. A signal processor receives the force and the displacement distance determinations from the electronic control module and analyzes these data to provide a visual data analysis indicating any lesion within the tissue.
There have been attempts to develop hand held self-palpation devices for sensing regions of hardening in breast tissue and thus mimicking manual palpation for detection of breast cancer. U.S. Pat. No. 5,833,633 issued to one of the inventors of the present disclosure, discloses a hand held pad comprising a pressure sensor array, data acquisition circuit, and microprocessor. Detection of nodules is achieved by analyzing the dynamic and spatial features of the pressure pattern while the probe is pressed to the breast and is periodically moved transversely to the ribs. U.S. Pat. Nos. 5,916,180 and 5,989,199 reissued to Cundari et al. describe several devices designated to assist the user in performing breast self-examination. These devices include an array of pressure sensors, electronic circuit and warning indicator. A plurality of processing tests is performed on the received signals from the pressure sensors, and different types of tissue structures are discriminated from each other based on the results of the tests.
While the above-described conventional devices may be valuable tools for breast cancer detection, the devices have certain limitations. Specifically, the conventional devices cannot be used for a regular home use in a repeatable pattern that allows for accurate serial studies. One of the reasons is absence of motion tracking system in the conventional self-palpation devices. Therefore, there is a continuing need for an improved hand held self-palpation device comprising a motion tracking system and corresponding methods for reproducible 3-D breast mapping.
Typical conventional motion tracking systems (magnetic, mechanical, optical, and acoustical) use interactions with another component of the device that is located a distance from the main part of the device being tracked. With a magnetic motion tracking system, a magnetic field transmitter is provided which is spaced from the magnetic field receiver mounted on the tracked device. With an optical or acoustical motion tracking system, light or sound sources are provided at a known location. Mechanical trackers are connected to a reference through an arm-like device. The above-described motion tracking systems do not provide a self-contained apparatus for mounting on the device to be tracked, which apparatus can track the trajectory and orientation of the device without interaction with radiation or energy from any other apparatus. Such a self-contained motion tracking system is desirable for a hand held self-palpation device.
Conventional navigation systems using accelerometers and gyroscopes or magnetometers have been used for ships, planes, missiles and spacecraft. This navigation system is a type of self-contained motion tracking system, as that term is used herein. The main problem with using accelerometer based motion tracking systems in different kinds of devices is drift. Drift arises from double integrating over time a signal that is noisy or has a bias which is sometimes compared with the signal. This problem can be solved for a particular application by taking into account the particular qualities of the described system. For example, U.S. Pat. No. 5,640,325, issued to Bandbrook et al. discloses a system, which uses silicon accelerometers and fiber optic gyroscopes for detecting the position and orientation of a towed array of acoustic sensors used for target detection. U.S. Pat. No. 6,205,401, issued to Pickhard et al., describes a navigation system for a vehicle having six-axis gyroscopes and two accelerometers in the horizontal vehicle plane. To reduce the noise and drift errors supporting signal devices, a satellite receiver is used. U.S. Pat. No. 6,162,191 issued to Foxin reveals the details of an inertial orientation tracker having automatic drift compensation for tracking the human head. The drift compensator includes a gravitational tilt sensor or an Earth""s magnetic field sensor. In all the above-described patents the received position and orientation data are processed over time by different Kalman filters to reduce the error in motion tracking determinations.
It is desirable to provide a hand held self-palpation device with 3-D self-contained positioning system for a regular home breast mapping which is easy to use and would facilitate regular self-examinations conducted by women, thereby leading to improvement in early detection of breast cancer.
The self-palpation device of the present invention utilizes the same mechanical information as obtained by manual palpation conducted by a skilled physician but objectively and with higher sensitivity and accuracy. The present method and device provides detection of tissue heterogeneity and hard inclusions by measuring changes in the surface stress pattern using a pressure sensor array applied to the tissue in the oscillatory mode along with motion tracking data analysis. Calculation of pressure sensor array trajectory and orientation comprises processing data received from a self-contained motion tracking system and correcting said trajectory and orientation via suitable Kalman filter using pressure response data from said pressure sensor array. An analysis of pressure response data for oscillatory deformations comprises cumulative summation of a plurality of pressure response frames after spatially shifting every frame by a pre-calculated amount taking into account direction of the pressure sensor array displacement. The present device and method determines mechanical and geometrical features of the breast inner structures by formation of a 3-D mechanical image of the breast combining results of local scanning at all breast sites using a calculated position and orientation data from the pressure sensor array.
The method and device in accordance with the teachings of the present invention enable the user to detect changes in the breast tissue that could be indicative of cancer development. The device of the present invention comprises a plurality of pressure sensors arranged in a two-dimensional pressure sensor array, a self-contained motion tracking system integrated with the pressure sensor array, and an electronic unit for providing acquisition of signals from the pressure sensor array and motion tracking system for processing, real time displaying, and storing received data. Detection of nodules is achieved by analyzing the dynamic and spatial features of the measured signals obtained by pressing the probe to the breast and oscillating it over the area under investigation.
The present invention provides a hand held self-palpation device for home breast investigation that generates reproducible 3-D images of the inner mechanical structure of the breast. It will become hereinafter apparent, the nature of the invention may be more clearly understood by referencing to the following detailed description of the invention, the appended claims and the several views illustrated in the drawing.